I am not sure I agree with that statement. Apple make a large chunk of money off the continual upgraded hardware sales. By selling an upgradeable Mac at a somewhat affordable price, end users would stop buying full systems from Apple in the volumes they currently do, and buy parts from 3rd parties which would slow down Apples' sales. Something they don't want. Apple make money on high value, large margin items.
Apple deny plenty from their customers in order to facilitate sales later.
hardware is so cheap it doesn't make sense to upgrade. by the time you finish penny pinching you could have bought a new system every few years for a lot less. the days of treasuring electronics for years are long gone